UV climatology at Palmer Station, Antarctica, based on Version 2 NSF network data Germar Bernhard * , Charles R. Booth**, James C. Ehramjian*** Biospherical Instruments Inc., San Diego ABSTRACT Spectral ultraviolet (UV) and visible irradiance has been measured at Palmer Station, Antarctica, between 1988 and 2004 with a SUV-100 spectroradiometer. The instrument is part of the U.S. National Science Foundation’s UV Monitoring Network. Here we present a UV climatology for Palmer Station based on the recently produced “Version 2” data edition. This data set will supersede the original release “Version 0”. Corrections applied to the new version increased biologically effective UV dose rates by 0-9%. Values of UV-A irradiance changed by –8% to +10%. A comparison with results of a radiative transfer model confirmed that measurements of different years are consistent to within ±5%. Total ozone column was calculated from UV spectra and was found to agree with measurements of NASA’s Total Ozone Mapping Spectrometer (TOMS) installed on the Nimbus-7 satellite to within 1%. TOMS measurements on the Earth Probe satellite are 3% lower than SUV-100 data. Effective surface albedo was estimated from clear sky spectra. Between August and November, albedo typically ranges between 0.6 and 0.95. After melting of snow and sea ice, albedo varies between 0.3 and 0.5. Biologically effective UV radiation is largest in November and December when low total ozone amounts coincide with relatively small solar zenith angles (SZA). During these months, the noon-time UV Index typically varies between 4 and 7, but UV indices as high as 14.8 have been observed. The largest erythemal daily dose of 8.8 kJ/m² was measured on 11/10/97 and 12/7/98. Linear regression analyses did not indicate statistically significant trends in UV or visible radiation, with the exception of February when small downward trends with statistical significance were observed. On average, clouds reduce UV irradiance at 345 nm between 28% (October and November) and 42% (February) compared to clear sky levels. In extreme cases, reductions by clouds can be as high as 90%. Between September and November, the variability introduced by ozone is similar to that caused by clouds. Keywords: Solar ultraviolet radiation, Antarctica, climatology, total ozone, albedo. 1. INTRODUCTION The National Science Foundation’s Office of Polar Programs (NSF/OPP) UV Monitoring Network was established in 1987 in response to severe ozone depletion reported in Antarctica. Biospherical Instruments (BSI) installed the first instruments in 1988 1 and has operated the network since. 2 The network currently consists of seven sites, which are mostly located at high latitudes. All stations measure global spectral irradiance between 280 and 600 nm with high- resolution SUV-100 and SUV-150B spectroradiometers. Further information on the network and its data is available at the website www.biospherical.com/nsf. Currently published network data are based on the originally released “Version 0” data set. This data set has not been corrected for deviations of the angular response of SUV-100 spectroradiometers from the ideal cosine response nor for wavelength errors of approximately 0.1 nm, which affect spectra measured before 1997. To improve the accuracy and homogeneity of network data, a new data edition named “Version 2” is currently being generated. Version 2 data are not “pure” measurements like Version 0 data, as radiative transfer calculations are used for the various corrections. These model calculations also provide clear-sky reference spectra during cloudy periods. Version 2 data from the instrument located at the South Pole (SPO) and McMurdo (MCM) were recently introduced. 3,4 Here we present the new Version 2 * bernhard@biospherical.com; phone 1 619 686-1888; fax 1 619 686-1887; http://www.biospherical.com; Biospherical Instruments Inc., 5340 Riley Street, San Diego, CA 92110-2621, USA; ** booth@biospherical.com; *** jime@biospherical.com Ultraviolet Ground- and Space-based Measurements, Models, and Effects V, edited by G. Bernhard, J. R. Slusser, J. R. Herman, W. Gao, Proc. of SPIE Vol. 5886 (SPIE, Bellingham, WA, 2005) · 0277-786X/05/$15 · doi: 10.1117/12.614172 Proc. of SPIE 588607-1